- Combustion chamber carbon deposits (with a rounded scraper)
Do not use a sharp instrument to avoid damaging or scratching:
- Spark plug bore threads
- Valve seats
2. Check:
- Cylinder head
- Dowel pins
Damage/scratches → Replace.
Replace the titanium valves with the cylinder head.
Refer to "Checking the valve seats".
Cylinder head water jacket. Mineral deposits/rust → Eliminate.
3. Measure:
- Cylinder head warpage
Out of specification → Resurface the cylinder head.
Warpage limit 0.10 mm (0.0039 in).
![](https://motoinstruction.ru/img/yamaha/20/126631.jpg)
a. Place a straightedge "1" and a thickness gauge "2" across the cylinder head.
![](https://motoinstruction.ru/img/yamaha/20/126632.jpg)
b. Measure the warpage.
c. If the limit is exceeded, resurface the cylinder head as follows.
d. Place a 400-600 grit wet sandpaper on the surface plate and resurface the cylinder head using a figure-eight sanding pattern.
To ensure an even surface, rotate the cylinder head several times.